1) Field of the Invention
The present invention relates to a semiconductor device and its manufacture method, and more particularly to a semiconductor device having transistors and capacitors connected to the transistors and its manufacture method, the capacitor being made of a lamination of a metal film, a dielectric film and a metal film sequentially stacked in this order.
2) Description of the Related Art
A capacitor is used as a memory element of a dynamic random access memory (DRAM). The performance of a memory element can be improved by improving the performance of a capacitor. It becomes easy to make DRAM compact if a capacitor is made of a capacitor dielectric layer having a high dielectric constant.
Ta2O5 is known as oxide dielectric material having a high dielectric constant. If a Ta2O5 film is used as the capacitor dielectric layer, leak current can be reduced. If a Ta2O5 film is formed by chemical vapor deposition (CVD), good step coverage can be realized.
If an oxide dielectric material layer having a high dielectric constant is used as a capacitor dielectric layer, it is desired that the lower and upper electrodes of the capacitor are made of metal which is not oxidized or remains conductor even if it is oxidized. Such electrode material facilitates to form a capacitor having good electrical characteristics. Rare metal which contains noble metal such as Ru and Pt is known as the material not oxidized or maintaining conductivity even if it is oxidized. Good step coverage can be realized if a Ru film is formed by CVD.
DRAM manufacture processes can be classified into a process of forming a transistor, a process of forming a wiring layer between a transistor and a capacitor, a process of forming a capacitor, a process of forming a wiring layer and a protective film on and over the capacitor, and a heat treatment for recovering the transistor performance. The heat treatment for recovering the transistor performance is performed in a hydrogen atmosphere. It has been found that if a heat treatment is performed in a hydrogen atmosphere, the electrical characteristics of a capacitor having a Ru/Ta2O5/Ru structure are degraded although the transistor performance is recovered.
The capacitor electrical characteristics can be recovered by performing a heat treatment for recovering the capacitor electrical characteristics at about 400° C. before a protective film of silicon nitride is formed. It is difficult to reduce leak current of a capacitor by a heat treatment after the protective film is formed.